The furnace walls in the modern thermal power boilers are usually relatively light water tube walls, which have a high tensile strength, but they do not endure much compression or bending. Thus, large thermal power boilers are usually supported from above, which means that the furnace of the boiler has been suspended to hang from a stationary bearing structure surrounding the furnace by means of hanger rods attached to the upper portions of the side walls of the furnace.
The main elements of the bearing structure usually consist of vertical pillars and horizontal main supporting beams supported on the top of the pillars or to the upper portion thereof, to which outer supporting beams of the bearing structure and the suspending structure of the furnace are supported. In some thermal power boiler plants, the main supporting beams form a grid above the boiler structure, which comprises main supporting beams, longitudinal and traverse relative to the furnace. The present invention, however, relates to a thermal power plant, having parallel main supporting beams supporting the boiler structures. The main supporting beams are usually 2-6 m high steel beams, for example, I beams, the length of which may be even more than 30 m, and which often weigh more than 100 tons. The main supporting beams are usually connected to other horizontal beams that are, however, smaller than the main supporting beams of that size.
There are other boiler structures that are integrated to the furnace of the boiler, especially, a back pass comprising heat exchange surfaces and channels for leading flue gas from the furnace to the back pass. The back pass and the flue gas channels leading thereto can be suspended to hang, according to the prior art, with the furnace from a shared supporting structure. The supporting structure of a thermal power boiler is generally a mainly right rectangular prism, and dimensioned in such a way that at least the furnace, flue gas channels, and back pass can be placed therein. Thus, the size of the supporting structure depends on the size of the holler structure and the mutual positioning of the parts thereof.
The height of a modern large thermal power plant is several tens of meters, typically, at least about 50 m. One factor adding to the height of the thermal power plant in accordance with the prior art is that a sufficient length is required for the hanger rods of the furnace due to the horizontal thermal expansion of the furnace.
The present invention especially relates to a thermal power boiler plant having flue gas channels arranged above the furnace. According to the prior art, the flue gas channels arranged above the furnace are suspended to hang from the main supporting beams, and, therefore, the height of such a thermal power boiler plant is especially high. One result of the flue gas channels being arranged above the furnace is that they also cause the hanger rods of the suspension structure of the furnace in accordance with the prior art to become long.
Long hanger rods are problematic, especially because the temperature of the hanger rods mounted to the upper portion of the furnace follows, to a certain extent, the temperature of the furnace walls, which causes relatively high thermal expansion of the hanger rods. Thus, the design of the supporting structure has to be such that the thermal expansion of the supporting beams does not cause any breaking of the boiler structures.
As the furnace walls do not endure heavy local forces, the distances between the hanger rods supporting the furnace from the supporting structure have to be small enough. Densely positioned hanger rods, however, make the use of the space above the furnace more difficult, for example, when arranging the flue gas channels above the furnace. Alternatively, it can be said that the flue gas channels above the furnace hinder the arrangement of hanger rods close enough to each other.